1. Field of the Invention
The present invention provides a three-axis magnetic bearing utilizing a permanent magnet to generate the bias flux and wherein the magnets are mounted to the face of the pole stack.
2. Description of the Prior Art
Copending application Ser. No. 09/865,015 filed May 23, 2001, invented by the inventor of the instant application, discloses and claims a magnetic thrust bearing using a single coil and linear amplifier and a single thrust desk. The design set forth in the copending application does not utilize permanent magnets, and more specifically, axially magnetized permanent magnets that are not attached to the rotor, for reduced cost and simplified construction when compared to existing thrust bearings.
Although the design set forth in the copending application provides significant advantages over the prior art designs described therein, it is desirable to provide a magnetic bearing wherein magnetized permanent magnetic members are utilized to provide the magnetic field for both the radial and axial axes to allow for radial and axial shaft position control. However, the system set forth in the copending application does not allow for active radial position control. Current techniques for manufacturing magnetic bearings using radial magnetized permanent magnets require costly and difficult assembly and alignment procedures.
What is desired therefore is to provide a magnetic bearing that utilizes axially magnetized permanent magnets wherein the fabrication, assembly and installation of the permanent magnets to the stationary stator is accomplished in a simple and inexpensive manner.
The present invention provides an improved magnetic bearing that uses permanent magnets to provide the bias flux with electromagnetic coils providing the control flux, bias flux being a constant magnetic flux which energizes the bearing airgaps. The control magnetic flux adds flux from one pole and subtracts flux from the opposite axis pole to produce a net force on a target piece located on the bearing shaft. Bias magnetic field is present to allow for linear control of force using the control input current, the input current being converted to magnetic flux by the control electromagnets in the magnetic bearing. Providing bias magnetic flux using permanent magnets reduces the required bearing input power (by eliminating a bias electromagnet) and provides a highly linear magnetic bias field in the airgap throughout the bearing radial and axial airgaps. The magnetic circuits generating the control and bias fluxes are substantially non-coincident but share a path over some portions that include radial and axial airgaps, allowing for a low reluctance, efficient path for the electromagnetic flux. The flux paths of the permanent magnets are completely defined with minimized airgaps for achieving higher forces, small size and minimum cost. The non-coincident control flux path allows for very low control currents to produce extremely large forces very efficiently. A single coil and amplifier for control of the axial force and two coils with one associated amplifier for each radial axis of control provides simplicity and cost effectiveness. A single target disk is utilized and is reacted against for both radial and axial forces. Radially magnetized permanent magnets are not required and permanent magnets are not attached to the rotor. The permanent magnets used in the present invention are first fabricated and then axially magnetized as square segments or as a ring prior to being mounted on the sides of the stator central pole, providing an effective and inexpensive technique for manufacturing magnetic bearings.